Processes for the preparation of such a catalyst component—as described, for instance, in WO 00/08073 and 00/08074—usually include a step in which a magnesium-Gp 4 metal-electron donor component is recovered by precipitation from solution, typically by contacting the solution with a large amount of an aliphatic hydrocarbon. However, such precipitation leads to a tar-like reaction product of low catalytic activity, that needs to be washed several times in order to decrease the amount of inactive Gp IVB metal complex. Aromatic hydrocarbons have also been used for the precipitation, but they lead to a very finely divided precipitate which is difficult to deposit. Worse still, it is difficult to carry out such precipitation in a controlled and reproducible manner, leading to unsatisfactory product morphology. Moreover variable and low concentrations of catalyst constituents such as butyl chloride may result, as a consequence of precipitation evaporative removal of aliphatic solvent.